Diffractive optical elements with varying direction for depth modulation

Abstract

In an optical display system that includes a waveguide with multiple diffractive optical elements (DOEs), one or more of the DOEs is configured with gratings that have varying depth and varying directions for depth modulation, in which the modulation direction is aligned with the steepest change (i.e., slope) of grating depth. Depth modulation direction may change at a point of transition between different regions in the DOE. For example, with a zero axis being defined along a line parallel to a long side of a DOE, the depth modulation direction can change from a negative angle, with respect to the axis in the plane of the waveguide in one region, to a positive angle in another region, or vice versa. By varying depth modulation direction in a DOE, display uniformity in the optical display system may be increased.

What is claimed: 
     
       1. An optical system, comprising:
 a substrate of optical material; 
 a first diffractive optical element (DOE) disposed on the substrate, the first DOE having an input surface and configured as an in-coupling grating to receive one or more optical beams as an input; and 
 a second DOE disposed on the substrate and configured for pupil expansion of the one or more optical beams along a first direction,
 wherein at least a portion of the second DOE includes two or more regions in which a depth modulation direction is constant within a region and changes at each transition between regions, the depth modulation direction described by a steepest change of grating depth in the second DOE, and 
 wherein the two or more regions in the second DOE do not include multi-level grating features. 
 
 
     
     
       2. The optical system of  claim 1 , further comprising a third DOE disposed on the substrate, the third DOE having an output surface and configured for pupil expansion of the one or more optical beams along a second direction, and further configured as an out-coupling grating to couple, as an output from the output surface, the one or more optical beams with expanded pupil relative to the input. 
     
     
       3. The optical system of  claim 2 , in which at least a portion of the first DOE or at least a portion the third DOE is configured with two or more regions in which a depth modulation direction changes at each transition between the regions. 
     
     
       4. The optical system of  claim 3 , in which at least the portion of the first DOE, second DOE, or third DOE includes gratings that are slanted. 
     
     
       5. The optical system of  claim 1 , in which the one or more optical beams received at the first DOE emanate as a virtual image produced by a micro-display or imager. 
     
     
       6. An electronic device, comprising:
 a data processing unit; 
 an optical engine operatively connected to the data processing unit for receiving image data from the data processing unit; 
 an imager operatively connected to the optical engine to form images based on the image data and to generate one or more input optical beams incorporating the images; and 
 an exit pupil expander, responsive to the one or more input optical beams, comprising a structure on which multiple diffractive optical elements (DOEs) are disposed, one or more of the DOEs being configured with gratings of varying depth,
 in which the exit pupil expander is configured to provide one or more output optical beams, using one or more of the DOEs, as a near eye virtual display with an expanded exit pupil, 
 wherein one or more of the DOEs is configured to include two or more regions in which depth modulation direction is different in each of the two or more regions, the depth modulation direction in a region being a direction for which a rate of change of grating depth is greatest, and 
 and wherein the two or more regions in the one or more DOEs do not include multi-level grating features. 
 
 
     
     
       7. The electronic device of  claim 6 , in which the exit pupil expander provides pupil expansion in two directions. 
     
     
       8. The electronic device of  claim 6 , in which grating depth in a region increases along the depth modulation direction. 
     
     
       9. The electronic device of  claim 6 , in which grating depth in a region decreases along the depth modulation direction. 
     
     
       10. The electronic device of  claim 6 , in which gratings are asymmetric. 
     
     
       11. The electronic device of  claim 6 , as implemented in a head mounted display device or portable electronic device. 
     
     
       12. The electronic device of  claim 6 , in which each of the one or more input optical beams is produced by a corresponding one or more sources. 
     
     
       13. The electronic device of  claim 6 , in which the structure is curved or partially spherical. 
     
     
       14. The electronic device of  claim 6 , in which two or more of the DOEs are non-co-planar. 
     
     
       15. A method, comprising:
 receiving light at an in-coupling diffractive optical element (DOE) disposed in an exit pupil expander; 
 expanding an exit pupil of the received light along a first coordinate axis in an intermediate DOE disposed in the exit pupil expander; 
 expanding the exit pupil along a second coordinate axis in an out-coupling DOE disposed in the exit pupil expander; and 
 outputting light with an expanded exit pupil relative to the received light at the in-coupling DOE along the first and second coordinate axes using the out-coupling DOE,
 in which the intermediate DOE is configured with at least two regions wherein a depth modulation direction in a first region of the at least two regions has a negative angle in a plane of the intermediate DOE with respect to a zero axis and a depth modulation direction in a second region of the at least two regions has a positive angle in the plane with respect to the zero axis, wherein depth modulation direction is described by a steepest change of grating depth in each respective region, and 
 and wherein the at least two regions in the intermediate DOE do not include multi-level grating features. 
 
 
     
     
       16. The method of  claim 15 , in which the zero axis is parallel to a long edge of the intermediate DOE. 
     
     
       17. The method of  claim 15 , in which the in-coupling DOE, the intermediate DOE, or the out-coupling DOE is formed with a polymer that is molded from a substrate that is etched using ion beam etching with a moving mask. 
     
     
       18. The method of  claim 15 , further in which at least a portion of the out-coupling DOE is an apodized diffraction grating having shallow grooves relative to the in-coupling DOE or the intermediate DOE. 
     
     
       19. The method of  claim 15 , as performed in a near eye display system. 
     
     
       20. The method of  claim 19 , in which the output light provides a virtual display to a user of the near eye display system.